help with subpannel

We recently bought a 1950's house that had an addition done in 2004. At that time the electrical service was relocated and upgraded to 200A. It seems as if the old main pannel located in the attached garage was converted to a subpannel fed off a 100A breaker in the main pannel. There was also another subpannel in the garage for the air handler fed off a 60A breaker in the main pannel. When we moved in an electrician added 2 new circuits for the kitchen. He added them to the air handler subpannel becuase access to the attic to get to the main pannel would have been very difficult. I then added one more circuit to that pannel for a garage receptacle and 2 exterior lights. From my reading, it seems as if subpannels in attached garages should have neutrals and grounds separated and be fed by a 4 wire feed from the main pannel. In my pannel there is only a 3 wire feed and the grounds and neutral share the same bar. I could move these circuits to the main pannel, but the access to the attic is terrible, although I will probably have to do that eventually. My question is- Is this a dangerous situation and why?

Thanks for your advice,
Mark

Main pannel:

Air handler sub pannel with kitchen and garage circuits:

Old main, now sub pannel for old part of house, dryer, water heater, range.

Thanks for the replies. You are correct the HVAC subpannel is fed by 2 hots and a ground. If I move all the 110 volt circuits to the main pannel and leave the 60 amp breaker in the HVAC pannel will that be acceptable as the air handler disconnect? The air handler is about 4 feet away from the pannel connected by flexible conduit. Will this then be up to code?

It appears that they used "entrance cable" to wire the subpanel, and that wire uses the exterior sheathing for the neutral by twisting it together into a cable. Your ground and neutral in the main panel are interconnected so the entrance cable is a "neutral" even though it is attached on the ground side. But, you do not have a dedicated ground wire for the sub panel circuits.